Television signal system



Nov. 21, 1939. A. F. MURRAY TELEVISION SIGNAL SYSTEM 2 Sheets-Sheet 1 Filed Jan. 11, 1936 Patented Nov. 21, 1939 1 UNITED STATES 2,181,064 TELEVISION, SIGNAL SYSTEM Albert F. Murray, Haddonfield, N. J., assignor to Philco Radio & Television Corporation, Philadelphia, Pa., a corporation of Delaware Application January '11, 1936, Serial No. 58,751

9 Claims.

This invention relates to television systems and the like and, more particularly, to improvements in reproduced pictures of such systems. The prncipal object of the invention is to provide a novel background pattern for the reproduced pictures bythe useof one or more artificial video signals.

Another object of the invention is to produce a reproduced picture of more pleasing appearance by electrically modifying the video signal formed in the usual manner.

A further object of the invention is'to supply an electrical background pattern signal to a television system or the like, by means of which due to thermal agitation in the vacuum tube amplifiers, may be minimized, particularly when the reproduced picture is faded out.

A still further object'of the invention is to addition to its primary function, may serveto convey additional intelligence from the transmitter to the receiver. d

The above objects are achieved by applying a telligence transmission channel of a particular system ,at any suitable point between the video signal generator and the picture reproducer.

The term intelligence transmission channel,

as used herein and in the appended claims, means the signal channel and includes only those ele'- ments of the system which participate directly in the signal transmission. It does not include elements outside the signal channel, such as the deflecting circuits. Thus, the auxiliary or background pattern signal may be applied to thetransmission channel at the transmitter and may be transmitted to the receiver along with the customary video signal, or the background patternv signal may be supplied to the transmission channel at the receiver. In any case, the background pattern signal will serve to produce a pleasing background pattern for the reproduced picture; The picture background pattern thus produced may take various forms depending upon the nature of the background signal, as explained in detail hereinafter.

The invention may be more clearly understood from the following detailed description in connection with the accompanying drawings illustrating certain specific embodiments.

In. the drawings:

Fig. 1 illustrates a preferred method of scanning and the formation of a picture background pattern in accordance with the invention;

signal the effect of random signals, such as those provide a background pattern signal which, in

wave signal-of predetermined frequency to the in-' point I, J, etc. In the figure, the lower frame Fig. 2 shows a picture area with a portion thereof shown in magnified detail, illustrating one form of picture background pattern which; may be produced by the invention;

Figs. 3 to 5 illustrate magnified picture back- 6 ground patterns of diflerent patterns which may be formed by the invention;

Fig. 6 is a schematic illustration of a complete television system embodying one form of the invention;

Fig. 7 is a similar illustration'of a television receiver employing another embodiment of the invention; and

Fig. 8 is a'similar illustration of a complete televisionsystem embodying a further form of the invention. I

It is well known at the present time in the art of photography that the quality or aesthetic appearance of a photograph may beimproved by reproducing such photograph on paper whose surface contains numerous small irregularities. This effect in photography is sometimes spoken of as the matte efiect and is used extensively toenhance the attractiveness of portraits and other such pictures. I have found that a similar 5 effect maybe obtained in a conventional, television system by the addition of certain electrical signals and that by the use of such signals other pleasing efiects may be obtained. In. a conventional television system, the image to be trans- 3o mitted is usually converted to an electric signal by means of some sort of scanning device such as a Nipkow disk or cathode ray camera tube. In this manner the visible image isconverted into an electrical signal which may be transformed 'back'to a visible image byfa similar scanning process at the receiver.

In a high definition television system,'interlaced scanning is usually employed. The method of interlaced scanning'is shown in Fig. 1, wherein the upper frame-represents the area being scanned. The lower frame illustrates the formation of the background pattern, as described hereinafter. The scanning spot may start at the point A, move across the image along the path AB to B at which point the spot is brought back to C from whence it goes to D etc., down the picture to the point E. At E it is returned to the point F from whence it travels toG thence to represents the path ofthe spot after the scan starting at A and ending at E has been completed. The actual path over the picture area is obtained by superimposing the two scans and in the figure the path in the lower scan is shown by mined by well known television phenomena. Only the dotted line in the upper scan. Thus it will be seen that the paths are interlaced as the scanning spot moves over the picture area, and an electric signal or a visible signal proportional to the intensity of light at the particular spot location is formed. In this manner an optical image may be converted into an electrical signal, which signal is a function of time, or vice versa. Further details of this figure are described hereinafter.

In the usual practice, the image to be transmitted is generated by scanning that image at the transmitter and converting the electrical signal thus formed back to an optical image at the receiver. I have found, however, that certain images may be formed electrically without recourse to scanning at the transmittenwhich images will add materially to the appearance of an image reproduced at the receiver by the usual means. For example, if the video or image signal generator at the transmitter is replaced by a generator of electrical signals of predetermined transmittable frequency a pattern corresponding to this signal will be reproduced at the receiver. Such a pattern, for example, is shown in Fig. 2 and may comprise a crossed line pattern made up ,of very small dark lines and light squares. If now, a television picture is superimposed upon this checkerboard pattern by means of transmission through the conventional system the resulting picture will be similar to the type known in photography as a picture having the above-mentioned matte effect, In other words, the aesthetic quality of the picture has been enhanced and its pictorial value increased.

By a signal of transmittable frequency is meant one whose cyclic character or some effect thereof may be observed at the signal reproducer, or in other words, a signal having a frequency of substantial transmission efficiency as deterby the use of such a frequency may the back ground pattern be formed. 1 1

In the formation of background patterns, suc as that illustrated in Fig. 2, it has been found that the signal frequency of the background signal should bear a certain relation to the scanning frequency. In the conventional television system employing scanning methods such as illustrated in Fig. 1, there are, of course, two scanning frequencies involved, viz. the horizontal scanning frequency and the vertical scanning. frequency, which are the frequencies of the scanning signals employed to move the scanning spot over the picture area horizontally and vertically. If the background pattern signal frequency is denoted by S and if the horizontal and vertical scanning frequencies are designated, respectively, H and V, the relation between the background pattern signal frequency and the scanning frequencies may be represented by the equation where m and n are whole numbers, and a is the number of interlacings or the number of times the spot moves from top to bottom in covering the entire area. It will be noted that the vertical scanning frequency for interlaced scanning, such as illustrated in Fig. 1, is twice the frame frequency-or the frequency of reproduction of the entire image. Thus a equals two for thisparticular case. Where m and n (or for interlaced scanning m and a-n) are whole numbers, the resulting pattern will be stationary or fixed with respect to the picture area or mosaic on which the television picture is formed. In general, the larger the values of m or n, the finer or smaller will be the constituent elements of the resulting background. The factor m may have any value which may be satisfactory in any instance, but preferably m will have a value within the range one-half to twice the number of scanning lines of the image or reproduced picture.

Due to the fact that the image or reproduced picture in a television system is formed by the motion of a small spot having finite dimensions, the picture appears as though reproduced on a surface ruled with a large number of fine lines running in a generally horizontal direction. Depending upon the size of the spot and distance between lines, these may appear to be dark or light lines ruled on the picture screen. Good definition may be obtained by adjusting the spot size so that fine dark lines of nearly invisible width are obtained. Under these circumstances, a signal producing dark vertical lines will, when magnified, appear as shown in Fig. 2. If the spot size is increased, the horizontal lines could, of course, be made to disappear. The dark vertical lines may be obtained, in accordance with the present invention, by applying to the television system a wave signal S, whose frequency is determined by taking a value of m in the above equation approximately equal to the number of scanning lines and by taking n equal to zero.

'These vertical lines in combination with the horibackground elements produced by the background signal during each successive horizontal traversal of the scanning spot will remain the same or in the same horizontal position. If, however, the background signal frequency includes a multiple of the vertical scanning frequency, as it will if n is some value other than zero, then thebackground elements, produced by the background signal, will appear in different positions in the successive horizontal scanning lines, such that sloping background lines will be produced.

In general, the slope of these background lines is expressed by the following equation height z2 1 I 31 length 11 aspect ratio where the height -and length in the equation are the height and length respectively, of the reproduced image and where the slope is downward to the left if the fraction is positive, assuming that the scanning is effected in the same manner that the English language is written or read, i. e. in successive lines from left to right, and from top to bottom.

The formation of sloping background lines may be more clearly understood from Fig. 1 wherein the total number of horizontal scanning lines in a complete scanning cycle is thirteen and there are two vertical movements of the scanning beam to return it during a cycle. The values of m and n are both three in this case, and it will be seen from Equation .1 that the number of cycles of the background signal per scanning cycle is forty-five assuming a frame frequency of one. A complete scanning cycle is represented by the solid horizontal scanning lines, and for the purpose of illustration, the cycle is shown extended over two contiguous scan areas. The points L represent the cycle terminations of the background pattern signal, the oblique lines sloping downward toward the left passing through the corresponding points L in the successive horizontal scanning lines. It will be seen that the cyclic character of the background signal will produce sloping lines such as those shown, and these lines together with the horizontal lines will form the background pattern. Thus, several cycles of the background signal are illustrated in the lower right hand comer, and it will be seen that each such cycle will produce a light area and a dark area and these areas will form sloping background lines, as shown by the lines through points L. The broken horizontal scanning lines represen'tthe superposition of the lower frame upon the upper frame which is effected by interlaced scanning. It will be understood, of course, that the illustration has been greatly simplified; in actual practice, the number of horizontal lines per frame would be much larger, for example, for good definition, the number might be of the order of magnitude of 350.

Thus, it will be seen that the invention may be employed to produce background lines of any desired slope. By this feature of the invention,

there may be produced various background designs, such as those illustrated in Figs. '3, 4 and 5. In Fig. 3 is shown in magnified detail the figure obtained by taking a wave signal of such frequency as to give a sloping line and by adjusting the'spot size to give no horizontal lines; It will be noted that by so doing a checkerboard pattern is obtained in contradistinction to the crossed lines of Fig. 2, where the spot size was smaller and the slope of the added signal vertical.

Thedegree of magnification is higher in 'Fig. 3. It will be understood, of course, that the solid black of Figs. 2 and 3 is not truly representative but merely shows the pattern contrast.

- In Figs. 4 and 5 there are shown magnified pathighly magnified, would, of course, show that the criss cross lines are not solid but are actually made up of small squares or rectangles offset with respect to each other. The lines of Fig. 5

were obtained by two signals of such frequencies as shown above to give the desired slopes. In Fig. 4 the coupling between the oscillators apparently modulated the resulting signal to pro ducetwo signals having frequencies S1,S==b-H:c'-V (b and c being whole numbers) independent of the light or shade in the transmitted picture and will thus more nearly represent the photographic matte effect than in the latter case where the video signal is modulated. in

which case the "matte" effect will be dependent upon the light value of the transmitted image. If desired, of course, a combination of these two effects may be obtained. Due to the fact that the transmission efliciency of the scanning spot decreases for the higher frequency, it is generally necessary to use a background pattern signal of greater amplitude than that which might be suggested from a consideration of conventional video signals. In general, it may be said that if the background pattern signal has a frequency of the same order of magnitude as the highest video frequency, then an appreciable matte" effect may be obtained by using a background pattern signal whose amplitude is about one-third the maximum video signal amplitude. The amount of "matte effect is,of course, a

matter of taste and may be varied by varying the amplitude of the background pattern signal. Preferably, the frequency or frequencies of the background pattern signal may be between 0.2 and 1.2 times the maximum video signal frequency.

'As stated above, when the frequency of the background pattern signal is determined from 7 numbers, the background pattern can be made to move or shimmer. In other words, if the background pattern signal frequency is chosen so that it is not a multiple -of the horizontal scanning frequency and is not equal to the sum of multiples of the horizontal and vertical scanning frequencies, then the vertical or sloping background lines will not be recurrently and successively reproduced in the same positions on the picture area or mosaic. Stated differently, successive re-v productions or frames of the background pattern will be slightly offset with respect to each other and, as a result, the moving or shimmering background pattern will be produced. If -a plurality of such signals are used, each of which has a frequency such that it will not be stationary,

then a background pattern efiect may be obtained which is similar to the efiect-known in the photographic art as the "watered sil efiect. The background pattern will appear to shimmer, dis- "solve, and reform and will generally dance about the image.

Another method of obtaining this effect is by causing the background pattern signal frequency to vary slowly abouta mean frequency S determined as above set forth. This may be done by modulating the frequency 8 with a frequency selected so as to give the desired variation of the frequency S. Thus, if the frequency S produces the sloping lines of Fig. l, modulation of this mean frequency-will produce instantaneous sloping lines on each side of those of Fig. l. The effect of this will be to cause the background pattern to dance or move back and forth, the pattern remaining generally, however, on the picture area, whereas the method above mentioned may cause the pattern to appear to move continually across the picture area. Thus, various effects may be obtained and may be used to meet the requirements in any particular case. ,One of the difficulties in present television systems is the disflguration of the image due to ran-- dom; signals nthe amplifier generated by the the grid, and anode circuits, etc. At the present time, this effect is known in. the art of sound reproduction as "noise signals. In television, the noise to signal ratio is considerably greater than that found in audio systems: due to the wide frequency ranges encountered and, due to the pe-' culiar effect of this noise or random signals, it is generally described in the art as a snow or snowstorm signal, the name being derived from the effect which the signal produces on the image, This effect is remarkably similar to a picture of a snowstorm, the signal causing little white spots to move up and down on the screen. The effect of a background pattern, for example, one such as the watered silk eflect, is to eliminate completely the snowstore probably by introducing a visible signal of greater contrast than that caused by the random signals. Thus, this background signal may be said to drown out visibly the snowstorm signal in the same manner that an audible signal will drown out audibly a noise signal. Consequently, the use of additional signals to form a background pattern upon which titles, fixed displays and the like, may be superimposed, not only has a certain pictorial value but likewise serves to increase the clarity of the picture. A particularly interesting effect is that mentioned above, where by changing the frequency at a slow rate, a moving background pattern or watered silk effect is obtained.

In Figs. 6 to 8, there are shown schematically different methods of applying the background pattern signal to a conventional television system. InFig. 6, there is illustrated a complete system comprising both the transmitter and receiver. The transmitter comprises a video signal generator I, a video signal amplifier 2, and a transmitter 3. The video signal generator I may comprise a conventional camera tube and associated amplifiers. The video signal amplifier 2 may comprise a plurality of amplifying stages, while the transmitter 3 may comprise conventional apparatus for modifying the video signal by the addition of blanking and synchronizing signals to form a composite signal in the manner well known in the art. This composite signal may be used to modulate a carrier wave signal which may be radiated in the conventional manner to the receiver or the composite signal may be transmitted to the receiver by direct wire transmission.

The synchronizing and scanning signals may be formed by the synchronizing and scanning signal generator 4 which serves to energize the scanning means at the video signal generator I and supplies the necessary signals: to the transmitter 3 to form the customary composite signal. This signal is received at the receiver 5 and is utilized to reproduce the picture by the picture tube 6, as well known in the art.

In accordance with the present invention, a background pattern signal generator I is provided at the transmitting stage and serves to generate one or more background pattern signals such as those above described. The background pattern signal generator may comprise one or more conventional oscillators adapted to generate one or more wave signals having the predetermined frequency or frequencies determined as above set'forth. The background pattern signal generator may be coupled to the synchronizing and scanning signal generator 4, as indicated in Fig. 6, or this coupling may be omitted. depending upon whether it is desired to have a 2,1e1,oe4

well-known "shot efiect, thermal agitation in fixed or moving background pattern. Due to the relatively large magnitude of scanning signals usually employed, it is possible to synchronize the signal generator I with the scanning signal generator 4 by simply placing the two devices side by side or by the coupling effect of the electric field set up by each device. If desired, a more positive and direct coupling may be employed. On the other hand, this synchronization may be dispensed with where it is desired not to synchronize the background pattern signal with the scanning signal by shielding the devices with respect to one another in accordance with known methods. Since signal generators of the types employed are well known in the art, it is deemed unnecessary to il ustrate them in detail.

The background pattern signal may be introduced into the video signal amplifier 2 by employing two input tubes V1 and V2 connected together so as to have a common load circuit. The customary video signal supplied by the generator I may then be supplied to the input of tube V1, While the background signal supplied by generator I may be supplied to the input of the other tube V2. The common load circuit of these tubes may be connected to subsequent amplifier stagds. Where tubes V1 and V2 and the subsequent tubes are operated as linear amplifiers, the background signal is, of course, added to the usual video signal. Where the tubes are operating as nonlinear amplifiers, however, a certain amount of modulation is introduced. It will be understood, of course, that a customary modulation circuit could be used instead of the dual input tube arrangement if it is desired to modulate one signal by the other.

The receiver 5 operates in the normal manner, the background pattern signal being supplied to the picture tube 6 along with the video signal and producing a background pattern such as above described.

In Fig. '7, the background pattern signal is shown applied to the system at the receiver. The receiver 9 maybe a conventional television receiver supplying video and scanning signals to the picture tube- ID. The background pattern signal generator H may comprise one or more conventional oscillators as in the system of Fig. 6. The background pattern signal generator may be connected to the receiver 9 so as to introduce the background pattern signal in any of the video frequency amplifier stages. This may be done by using .the dual input tube arrangement of Fig. 6. Here again, the background pattern signal generator if desired may be synchronized with the scanning signals which are separated from the video signal in the receiver.

As previously stated, in addition to its primary function of producing a background pattern, the background pattern signal may be used to convey some form of intelligence from the transmitter to the receiver. This may be done by modulating the background pattern signal with the said intelligence. In general, it may be said that erable frequency for the background pattern sig-. nal may be from 0.5 to 3 mega'cycles. Assuming then that a signal of 2.8 megacycles is selected, it

is then possible to modulate this signal, for example, with audio signals, select this signal at the receiver by means of tuned circuits, detect the signal, then reproduce the transmitted audio signal.

In Fig. 8, there is illustrated a complete system in which the background pattern signal is employed additionally to transmit'an audio signal. A 'video signal generator l2 supplies the customary video signal to the composite signal amplifier [3 which, in turn, supplies'a signal to the transmitter M. The video signal generator and the composite'signal amplifier are each energized by the synchronizing and scanning signal generator I5. In a conventional television system, the usual practice is to transmit one line of video signal and then interrupt this signal for a brief interval to transmit a synchronizing signal. Thus, it will be seen that the composite signal comprises, first, a video signal and then a synchronizing signal, then a second video signal, etc. The modulated background pattern signal may be introduced in the chain before or after the formation of the composite signal. If it is introduced in the system before the composite signal is formed, it will be interrupted at'intervalstoallow for the introduction of the synchronizing signal.

On the other hand, if it is introduced after the formation of the composite signal, it

will be transmitted continuously but will tend to modify the form and wave shape of the synchronizing signal. I have found, however, that where a high frequency background pattern signal, such as those above described, is used, and

where such background signal has a relatively small amplitude, the synchronizing signal is not materially modified and will serve to perform its desired function regardless of the presence of the background pattern signal.

In the system of Fig. 8, the background pattern signal is generated by a suitable generator l6 comprising an oscillator and an audio signal is sup-,

plied by any suitable-source l'l. These two signals are combined in a modulator l8 to form a modulated background pattern signal which is supplied to the transmitter after the composite television signal has been formed in the unit l3. The complete signal thus-formed comprising the conventional composite television sig-' nal combined with the modulated background pattern signal maybe modulated upon a carrier wave .in the usual manner'and radiated to the receiver.

The receiver may comprise an amplifier stage l9 which supplies signal to the detector and video signal amplifier which, in turn, drives the usual picture tube 2|. The video signal amplifier 20 may also supply signal to an amplifier 22 comprising one" or more tuned amplifiers which select signals of the background signal frequency and reject other signals. The selected and amplified modulated backgroundpattern signal may then be detected and the audio signal may be amplified in the audio frequency amplifier 23 and may be supplied to a conventional loud speaker 24. The selection and, detection of the modulated background signal may be'accomplished by tuned amplifier and detector stages such as illustrated schematically in the diagram of unit 22. As mentioned above, the background pattern signal frequency may be higherthan the maximum video signal frequency originating in the original picture, then since the background method by which the pictorial value of a television image maybe improved or enhanced by means requiring only electrical apparatus, a. method by which the effect of random voltages inherent in electrical systems may be minimized, and further a method by whichin addition to the above-mentioned advantages, additional'intelligence may be conveyedirom the transmitter to the. receiver ,and if desired, such intelligence may take the form of speech,'music', or other audible signals. I am aware that it has been proposed heretofore to employ a background control signal the purpose of which is to control the average illumination of the screen on which the picture is being reproduced. Such a system is disclosed in the copending application of F. J. Bingley, Serial No. 51,324, filed Nov. 23, 1935. The background patterr signal of the present invention should not be confused with the background control signal. The two signals produce diiferent effects, are intended for different purposes, and require different frequency characteristics. It will be understood, of course, that modifications of the invention may be made, for example, as mentioned above, a plurality of background pattern signal components may be used and some of these signals-may have frequencies such as will form stationary patterns, whereas others may have fixed frequencies such as to cause uniformly moving patterns or such signals may be frequently modulated by which patterns ofthe watered sllk 'type may be obtained. Further it will be understood that any or all of said signals may be modulated and used to convey intelligence of some form or other from a transmitter to a receiver.

It is important to note that in addition to the above uses and advantages, the invention is adapted for the reproduction of a characteristic or distinctive pattern which may convey a certain meaning to'an'observer. For example, the pattern may identify a certain commercial article or company manufacturing, the same, thus adapting the invention to commercial advertising or other purposes.

From the above description, it will be understood that the term background pattern signal, employed herein and in the claims, means a signal which is capable of producing a'visible background pattern in the reproduced picture.

1. In a television system employing a video signal generator. including a camera tube and channel at a pointsubsequent to the camera tube and ahead of the video signal reproducer, and

means at the receiving station for demodulating said wave signal.

2. In a television system, including a transmitting stationand a receiving stationtherebeing a video signal generator including a camera tube at said transmitting station, and in which a certain scanning frequency is employed, apparatus for producing a background pattern for reproduced intelligence while transmitting additional intelligence, comprising means independent of said video signal generator for producing'a background pattern wave signal having a transmittable frequency bearing a predetermined relation to said scanning frequency, means at said transmitting station for modulating said wave signal with intelligence, means for transmitting said modulated wave signal along with the video signal, and means at said receiving station for demodulating said wave signal.

3. In a television system, including a transmitting station and a receiving station, there being a video signal generator including a camera tube at said transmitting station, and in which a certain scanning frequency is employed, apparatus for producing a background pattern for reproduced intelligence while transmitting additional intelligence, comprising means independent of said video signal generator for producing a background pattern wave signal having a transmittable frequency bearing a predetermined relation to said scanning frequency, means at said transmitting station for modulating said wave signal to a relatively small degree with intelligence, meansfor transmitting said modulated wave signal along with the video signal, and means at said receiving station for demodulating said wave signal.

4. In a television system employing a video signal generator including a camera tube and in which a certain scanning frequency is employed,

apparatus for producing a background patternfor reproduced intelligence, comprising means independent of said video signal generator for producing a background pattern wave signal having a transmittable frequency bearing a predetermined relation to said scanning frequency, means for modulating said wave signal frequency with a frequency such as to cause said wave signal frequency to vary about its predetermined value,

and means for applying said modulated wave.

signal to the intelligence transmission channel at a point subsequent to the camera tube and ahead of the video signal reproducer.

5. In a television system having a video signal transmission channel and employing a certain scanning frequency, the method of producing a uniform background pattern in the form of a matte effect over substantially the entire picture area, which comprises generating a continuous sine wave signal having a frequency related to said scanning frequency and having a value such that the signal may be electro-optically converted intoa visible image, and applying said wave signal to said video transmission channel so as to combine the said wave signal with the video signal, thus causing the combined signals to be electro-optically converted by the picture-reproducing device, the relation of said wave signal frequency to said scanning frequency being such as to produce a uniform matte effect over substantially the entire reproduced picture area.

6. In a television system having a video signal transmission channel and employing a certain scanning frequency, apparatus for producing a uniform background pattern in the form of a matte effect over substantially the entire picture area, comprising a continuous sine wave generator adapted to generate a wave signal having a frequency related to said scanning frequency and having a value such that the signal may be electro-optically converted into a visible image, and means for applying said wave signal to said video transmission channel so as to combine the said wave signal with the video signal, thus causing the combined signals to be electro-optically converted by the picture-reproducing device, the relation of said wave signal frequency to said scanning frequency being such as to produce a uniform matte effect over substantially the entire reproduced picture area.

7. In a television system havinga video signal transmission channel and employing a certain scanning frequency, apparatus for producing a uniform background pattern in the form of a matte effect over substantially the entire picture area, comprising a continuous sine wave generator adapted to generate a wave signal having a frequency related to said scanning frequency and lying within the range 0.2 to 1.2 times the maximum video signal frequency, whereby said wave signal may be electro-optically converted into a visible image, and means for applying said wave signal to said video transmission channel so as to combine the said wave signal with the video signal, thus causing the combined signals to be electro-optically converted by the picture-reproducing device, the relation of said wave signal frequency to said scanning frequency being such as to produce a uniform-matte effect over substantially the entire reproduced picture area.

8. In a television system having .a video signal transmission channel and employing a certain scanning frequency, apparatus for producing a uniform background pattern in the form of a matte effect over substantially the entire picture area, comprising a plurality of continuous sine wave generators each adapted to generate a wave signal having a frequency related to said scanning frequency and having a value such that the signal may be electro-optically converted into a visible image, and means for applying said wave signals to said video transmission channel so as to combine the said wave signals with the video signal, thus causing the combined signals to be electro-optically converted by the picture-reproducing device, the relation of each wave signal frequency to said scanning frequency being such as to produce a uniform matte effect over substantially the entire reproduced picture area.

9. In a'television system having a video signal transmission channel and employingtwo scanning frequencies, apparatus for producing a uniform background pattern in the form of a matte effect over substantially the entire picture area, comprising a continuous sine wave generator adapted to generate a wave signal having a frequency such that the signal may be electro-optically converted into a visible image and determined by the equation S=m.H-|-a.n.V, where S equals the said wave signal frequency, H equals one scanning frequency, V equals the other scanning frequency, a is the number of interlacings and m and n are whole numbers, and means for applying said wave signal to said video transmission channel so as to combine the said wave signal with the video signal, thus causing the combined signals to be electro-optically converted by the picture-reproducing device.

ALBERT F. MURRAY. 

